my case is weird

i have a line applied 2 years ago... the base speed is 1.5mbps and i manage to archive it

another line, just apply 3 months ago, the base speed also get 1.5mbps , but i will never archive even 1.0mbps

same house, same copper line , infact the new line are using new copper cable too...

new line always get sux ip
old line always get 60.48 or 60.50